The demand for ever faster and more complex signal and data processing in diverse fields of application has fuelled the need for new generations of signal processing systems having multiple high-performance ULSI circuits (e.g. processors, ASICs and FPGAs), which are characterised by their need for multiple low supply voltages, high levels of current demand and tight supply voltage regulation requirements. These needs are met by the so-called Intermediate Bus Architecture (IBA) power supply, which may provide a number of tightly-regulated voltages from an input power source via a two-stage voltage conversion arrangement.
FIG. 1 is a schematic of a conventional IBA power supply. The IBA power system 10 is a two-stage power distribution network comprising a first stage DC/DC converter 20 connected to an input power bus 30, which is typically at a voltage VDCH between 36-75 V, 18-36 V or 18-60 V. The first stage DC/DC converter 20 is connected via the Intermediate Voltage Bus (IVB) to the inputs of a number (K) of second stage DC/DC converters 50-1 to 50-K.
The first stage DC/DC converter 20, commonly referred to as an Intermediate Bus Converter (IBC), is preferably an isolated DC/DC converter. An IBA power supply having such a first stage DC/DC converter has the advantage of being more efficient and more cost-effective to manufacture by reason of the isolation from the input power bus, which generally requires the use of relatively costly components including a transformer, being provided at a single converter. Naturally, the IBC 20 may alternatively be non-isolated from the input power bus 30. The IBC 20 is typically implemented in the efficient form of a switched mode power supply (SMPS), which may be fully regulated or line regulated to convert the input power bus voltage VDCH to a lower intermediate bus voltage VIB on the IVB. However, in the interests of maximising the efficiency of the IBC, the IBC is typically chosen to provide an unregulated output voltage, taking the form of a fixed voltage conversion ratio DC/DC converter. Thus, the IBC 20 provides a fixed voltage conversion ratio (i.e. input-to-output ratio), most commonly 4:1, 5:1 or 6:1.
In the example of FIG. 1, each of the plurality of second stage DC/DC converters 50-1 to 50-K is a non-isolated buck regulator commonly referred to as a Point-of-Load (POL) converter or regulator, or a Point-of-Source regulator. In general, each of the second stage DC/DC converters may be isolated or non-isolated. However, where isolation is provided by the IBC 20, the POL regulators are preferably all non-isolated. A second stage DC/DC converter may take the form of an SMPS or a non-switched linearly-regulated Low Drop Out (LDO) regulator. Each POL (k) delivers a regulated voltage Vout—k to its load 60-k. In the example of FIG. 1, POL regulators 50-1 and 50-2 deliver power to a common load 60-1 (although, naturally, more than two POL regulators may deliver power to a common load). With the step-down ratio of the IBC 20 fixed at a pre-selected value, the voltage VIB on the IVB will of course vary with changes in the input voltage VDCH, thus requiring the POL converters to be capable of operating over a range of input voltages, for example 3-15 V.
Although the IBC 20 and the POL regulators 50-1 to 50-K are buck regulators in the example of FIG. 1, their topology is not limited to such and may alternatively be Boost, Buck-Boost etc.
Efficiency is, of course, a critical parameter of any power supply system. The prevailing approach to improving the efficiency of IBA power systems has been to maximise the efficiencies at which the individual converters, i.e. the IBC 20 and POL converters 50-1 to 50-K, operate under typical load conditions. As noted above, designers have sought to increase the efficiency of the IBC by dispensing with voltage regulation altogether, thus avoiding the associated burden placed on the input power bus or other power source by the required regulation circuitry, and allowing the IBC to operate at an optimum duty cycle. The voltage conversion ratio of the IBC is consequently fixed. Since the POL converters operate most efficiently and reliably with a limited ratio between their input and output voltages (i.e. VIB and Vout—k, respectively), the fixed value of the IBC's conversion ratio is selected such that the intermediate bus voltage VIB output by the IBC during expected operating conditions falls within a range of values at which the POL converters are able to operate most efficiently.
Despite the successes of the above approach, there still remains a need to improve the efficiency of IBA power systems.